Composite materials are increasingly replacing metals in aerospace structural applications due to their high strength and low weight. Composite materials may also be co-cured into large, complex, integrated structures, potentially reducing weight, manufacturing costs, and fastener counts. However, these complex integrated structures are often difficult to adequately inspect because critical inspection locations are closed-in and inaccessible to existing non-destructive inspection (NDI) equipment available in the industry.
This problem commonly occurs when hollow “hat”-type stringers run through the interior of a structure and are therefore not accessible for inspection by conventional means. Inspecting aircraft stringer-rib bond lines is particularly difficult using known methods.
One known method for inspecting tubular structures, such as water pipelines, includes the use of pipeline inspection “pigs” configured to inspect inaccessible tubular structures from the inside. These pigs operate in a liquid-filled environment and are moved via fluid flowing within a pipeline with no independent means of positioning. These pipeline pigs are designed to operate in completely filled pipelines and do not provide a way of limiting immersion fluids to a specific area under inspection. Various other known methods for inspecting stringers at least partially from the inside are generally not suitable for immersion inspection techniques, such as the immersion inspection methods with pipeline pigs.
Accordingly, there is a need for an improved method of inspecting composite parts that overcomes the limitations of the prior art.